When you talk about something with your friends, lots of topics are already happened before. In the case, you need to use past tense instead of present tense. Most foreigners learn present tense first. So when they adopt to learn past tense after present tense, they have hard time to change it. Let me give you brief explanation how to change it. There are three kinds of verb in Korean: descriptive verb, action verb, and 이다 verb. For D.V and A.V, you can mostly use this grammar rule “V.S. + 아/어+ㅆ+다/요”. Please read examples below.

To eat/ 먹다/먹었다-먹었어요 (먹었다 is infinitive of past tense. You need to change it to 요form which is speaking form)

To wear/ 입다/입었다-입었어요

To sleep/자다/잤다-잤어요

To be pretty/예쁘다/예뻤다-예뻤어요

To be hurt/아프다/아팠다-아팠어요

Only when there is ending consonant, use the 아/어 as you see the above examples.

Irregular: To sing/부르다/불렀다-불렀어요