If you know what’s the mark, remove it. If you don’t know what’s the mark, you may try to guess, but you can never be sure you actually removed it.
If you have no idea what you are looking for, your only chance to achieve any signifcant degree of confidence is to destroy a great amount of your file, most probably making it useless. As BobbyB pointed out in the previous discussion, the mark could be a single bit change, so to remove any possible mark you’d have to change every bit.