Here's how to change your primary account in the SentBe app.
How to change
1. SentBe app → MY → Verification Info → select the My Accounts tab
2. Deselect the ⭐ (star) on your current primary account
3. Tap the ⭐ (star) on the account you want to make primary
After the change, that account will be set as your default transfer account.