I used to run speech and language interventions with small groups in reception. Some things to remember are
Always model.
Repeat what the child says using the correct phrase, as other posters have said.
Repeat the same activity on different occasions. You can vary the activity by introducing some different vocabulary, but don't change all of it at once.
Don't worry about this at all, he will get there, but if you want some ideas, these are a couple of activities I have done to practise the past tense.
I used to play Simon Says, and after two turns I'd stop and ask, "What did you do?"
[Adult] Simon says jump.
Simon says touch your toes.
What did you do?
[Child] I jumped and touched my toes.
I also set up a teddy and various things for teddy to do - apple, cup, pencil and paper, ball, book, car etc. Then (after I'd modelled it) each child had a turn to make Teddy do something and tell us about it, eg, "Teddy ate the apple."
The next step was for the first child to make Teddy do two things and then ask the second child, "What did Teddy do?" Hopefully the second child would reply, "Teddy drank the juice and kicked the ball." Whether they got it right or not, I always repeated the correct version for all the children to hear.