As far as I can tell it's not clearly defined whether a tape of the TM is infinite on both sides or just one. For my example I am assuming that it is infinite on the right, which, if I am not wrong seems to be the most common case.
I start reading my string assuming it is on the very beginning, however, after I do some changes to my string like converting all the 0's to x's how do I come back to the very beginning? I can't just do $0, X, L$ (when you see $0$ replace with $X$ and move Left because left might be undefined and if my understanding is correct in that case the during machine Halts, as in it halts and it can't continue operation to possibly come to an accepting state.
After I travel right to left on the tape, how do I come to the beginning cell? One idea is to overwrite the initial string with blanks and then paste the string to the end so that I have a sentinel $\textbf{Blank}$ on both sides but there must be a simpler way to do this.
Any ideas?