Do the letters and numbers have any semblance to some format you might recognize, like base58 address, private key WIF, hexadecimal, something that might look like an ID or page number, and such? 
Without knowing it's format, you can't attempt any kind of recovery with the data.
This tool is not useful for OP because he doesn't have a damaged QR code, just a bunch of characters that came from one.
Without knowing it's format, you can't attempt any kind of recovery with the data.
Try this: https://merricx.github.io/qrazybox/
This tool is not useful for OP because he doesn't have a damaged QR code, just a bunch of characters that came from one.
It's a letternumber;letternumber;letternumber; then a string of numbers.....
All format mentioned by @NotATether using both letter and number. For reference, here are character used by each format
1. Hexadecimal/hex. Basically 0-9 and A-F
Code:
0123456789ABCDEF
2. Base58/WIF. Basically 0-9, a-z and A-Z, excluding "0" (zero), "O", "I" (big i) and "l" (small L)
Code:
123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
3. Base64. Basically 0-9, a-z, A-Z, "+", "/" and "="
Code:
0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+/=