I have pain in mMy left knee hurts and this started when I arrived in Perúu after my trip around the world.

I have pain in my left knee —> My left knee hurts (just a more natural option, but completely optional)
Start —> started
Arrive —> arrived
(Talking about the past with those two situations, so use past tense of the verbs)
English doesn’t really have accents on a lot of words unless they have been completely borrowed from another language so it doesn’t have its own English version without accents.

In the last 4 months I didn´’t need to run because ion the ship Wwe only needed to go up on the masts.

In 4 months —> in the last 4 months (I think it might be better to add “the last” to clarify that you’re talking about the past, as “in 4 months” implies that you’re talking about an event happening in the future, or more specifically, four months into the future the next events will happen)
In —> on (you would use on with ships)
(“We” is never capitalised unless it is at the start of a sentence. The only subject that this doesn’t apply to is “I”, which is always capitalised. Every other subject, however, is only capitalised at the start of a sentence).
Need —> needed (past tense. Need wasn’t put into the past tense earlier because “did” in “didn’t” already showed that it was in the past tense)
(I added in “to go” because you would need another verb between “needed” and “on the masts”. I deleted “on” just to match after adding in “to go”)

Well, to continue the explicanation: When I joined the battalion this year to continue my studies , I didn´’t practice to run and thrunning. This is a problem beacause I need aprove my control of physical effort.to…

Explication —> explanation (explication isn’t really used much, only really when analysing something in depth)
To run —> running (it’s hard to explain the reasoning but “running” is more natural)
This a —> this is a (you need a verb, which in this case is “is”. If the knee is no longer an issue, then you would use “was” instead.
(I was confused by “I need aprove my control of physical effort”)

And fFor two weeks I have been going to the academy´’s healthcaredoctor/nurse.

It’s better not to start a sentence with “and”.
“Healthcare” is more of a non-tangible concept or service relating to health, and isn’t something that you can really go to.

PA pain in my knee

I have had pain in my left knee and this start when Isince arriveing in Perú afterduring my trip around the world.

InFor the 4 months of my ocean voyage, I didn´t need to run because in the ship WeI only needed up on theattend to the ship masts.

Well, to continue the explication When I joined the battalion this year to continue my studies I didn´t practice to run and this a problem beacause I need aprove my control of physical effort.SUGGESTION: I could not understand this sentence. Could you write the original in Japanese or Chinese?

And for two weeks I have been going to the academy´s healthcareMY GUESS: And for the last two weeks I have been receiving healthcare from my facility.

I have pain in my left knee and thisthat started when I arrive in Perú after my trip around the world.

InFor 4 months I didn´t need to run because ion the ship Wwe only need to be up on the masts.

Well, to continue the explication When I joined the battalion this year to continue my studies, I didn´t practice to rundo any running and this a problem beacause I need aprove my control of physical effort. physical approval done

Im not sure if this is what you are trying to say but changed to what i thought sounded better :)

And fFor two weeks I have been going to the academy´s healthcare

could also use hospital or urgent care to replace "healthcare" when talking about the physical location