Assuming your table is called something like
fortranTable = Flatten[Table[
"STRING_" <> ToString[i] <> ToString[j] <> ToString[k] <> " = " <>
ToString[myTable[[i, j, k]] // FortranForm],
<> is the concatenation operator for strings, so I'm just converting the indices to strings and then joining them together. I have an expression like x^26 in position 111, I get:
STRING_111 = x**26.
If you want to export the final table, the following works but tweaks can be made depending on exactly what you want the output to look like.
I believe you can use either double backslashes
\\ to separate the parts of file names or a single slash, and of course
filename should be changed to suit your needs, but the quotation marks are required. This should give you a file where each entry in the table has its own line (that is, they're separated by '\n').