My 7 month old sleep who’s in a cot has started to roll on to his side and then on to his tummy while his asleep multiple times a night. Ive been turning him back over to his back which is interrupting both his and my sleep. Is there something that I can do to avoid this happening.

Most babies will be rolling over by 4- 5 months. Some earlier, some later.
This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their side or tummy.
This is not something that needs to be stopped. It is important to make the “new” environment as safe as possible.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

You have already adapted your baby’s sleep environment for rolling.
Moved from bassinet to cot.
Arms free - no swaddle or wrap.
Now that he is rolling well, continue to place him on back for sleep. & allow him to find his own position of comfort.
Ensure the mattress is firm, well-fitting & flat with nothing soft or padded.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over