> What I don't know how to do, nor find on Google,is turn off a specific bit whether it is set or not.

you "mask" (using & the "bitwise-and") with a bitvector which is only 0 if and only if you want to turn off.

DB<22> $in   = 0b10101010                                             
+                                                                     
+                                                                     
+                                

DB<23> $mask = 0b11110000            # 1 keep 0 erase                 
+                                                                     
+                                                                     
+                                                 

DB<24> printf "%b", $in & $mask                                       
+                                               
10100000
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for more see Mask (computing)