Assume you have the Set/Reset command in r7 and the bit address in r6 (00-3F).

setcmd equ XXh

dobits:
. mov a,r6
. anl a,#11111000b
. rr a
. rr a
. rr a
. add a,#20
. mov r0,a ;point to bit byte location
. mov a,r6
. anl a,#00000111b
. rl a
. movc a,@a+pc
. ajmp skip
. db 01h,02h,04h,08h,10h,20h,40h,80h
skip:
. cjne r7,#setcmd,rescmd
. orl a,@r0
. ajmp done
rescmd:
. cpl a
. anl a,@r0
done:
. mov @r0,a
. ret