Instagram Account Warmup is the process where you increase the amount of messages you send every couple of days to avoid bans.

Here's an optimal structure of how to take a new account to sending DMs:

Week 1:
5-15 DMs per day

Week 2:
15-20 DMs Per Day

Week 3:
20-35 DMs Per Day

Week 4:
35-40 DMs Per Day

Week 5:
40-50 DMs Per Day

Week 6:
50+ DMs Per Day