Battery Health / Maximum Capacity will decline on average at about 1% a month. That's a average though. Some months it might not decline at all and then drop 2-3% the next month.
If you purchased your phone in April 2023, the phone is now 9-10 months old. So, it would be expected for the Battery Health / Maximum Capacity to the be in the 88-91% range at this time. This is normal.
Apple will not replace the battery unless Battery Health / Maximum Capacity has dropped below 80% in the first year, so your battery would need to drop another 9% in the next 2-3 months to qualify for a replacement.
In 2-3 months, your battery will likely be at 85-87%.