If the problem is really that you only want to do this to the first two fields, the previous replies cover that.

But if you mentioned "first two matches" in reference to the specific sample data you show, and the underlying general problem is that you want to remove \d_ from the beginning of any and all /-separated fields in a string, then try:

    s#(^|/)\d_#$1#g;
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The (^|/) alternation matches at the beginning of the line or after your field separator, which avoids inadvertently matching and remove \d_ from the middle of a field.