Use your dictionary for irregular verb forms. think | θɪŋk | verb (past and past participle thought | THôt | )

For past tense, only use "was" with adjectives. Today I am happy. Yesterday I was happy. For verbs, use verb2 I am running now. I ran yesterday. We DO occasionally put "was" in front of a verb, but that is a much more advanced structure called "passive voice." I ate the apple yesterday. The apple was eaten yesterday.

'think' is an irregular verb. So there is no '-ed' version of it. Think - Thought

You cannot say "I was think" or "I was thinked", in fact the word "thinked" doesn't even exist, you can say "I was thinking". "I thought" is okay.