Anonymous
Suppose the probability of Tail is p and Head is (1-p). Adjust the weight of each Tail to be 1/2p and Head to be 1/2(1-p). Every time a Tail tossed is counted as 1/2p Tail, every time a Head tossed is counted as 1/2(1-p) Head.
In this case, the probability of tossing a Head will be 1/2, same as a Tail.