Je'ai passé un examen et je pense que ça s'est bien passé/c'était bien.

The auxiliary verb is missing to build the passé composé => j'AI passé
Subordinating conjunctions are compulsory => je pense QUE...
ça s'est bien passé = it went well

Je suis rentréer à chez moi et je viens de cuisiner le dîner.

"rentrer", like all reflexive verbs, require "être" as an auxiliary => je suis rentréE (the past participle agrees with the subject when it comes with "être")
rentrer quelque part

Maintenant, je vais réviser/étudier pour un autre examen dans le[demain matin. ?]

réviser = reading your lessons once again in the specific perspective of passing an exam
"dans le matin" means "at some (unspecified) point in the morning", which would leave any reader wondering: which morning?
If you're talking about tomorrow morning, this would be "demain matin"

Merci pour toivos corrections.

You're addressing a group here so you have to use the possessives corresponding to "vous". They are "votre" (singular), "vos" (plural)