Question

convert i am going to bed to past indefinite tense

Answer 1

i went to bed last night

Answer 2

To convert  "I am going to bed"  into past indefinite tense.

I went to bed.

Past indefinite tense is the same as simple past or past simple. We do not know the timing of the  action of the verb in the past. That is why it is indefinite past tense.

So we use the simple past tense of the verb "to go".