Changing your phone number doesn’t affect Between in any way. Continue using Between as you did prior to changing your number (using the same device).
Your partner will need to click on your profile from their Between screen to update your phone number, and vice versa if your partner is the one who has a new number.
※Caution
1. Please don’t create a new ID or disconnect with your partner.
2. Be sure to remember your ID and password. If you forgot your ID you can check it on your partner’s app.