This is a very simple hack to allow the game to start from P1's start button instead of P2.

One single value is changed at offset A9C from F7 to F6 to accomplish this. Forum user elbobelo also recommended changing offset A96 in a post, but this appears to be unnecessary.

The original information I found for this was here: https://www.romhacking.net/forum/index.php?topic=14115.msg204832