It should be accept suggestion to allow it. The AMS signatures have a Learn option under them but for violations is different.
If you have issues learning signatures check if the automatic policy builder is enabled for the ASM policy and and check under signatures that the ""learn"" checkmark is enabled for the specific signature id:
If the policy builder is enabled then check for bugs:
Maybe even a restart of the device may fix this. You may just restart the ASM process but better a full reboot as I had such issue before.