To relevel, you can youtube "flattening sharpening stone." people use a portion of a flat cement sidewalk to $20 to $50 flattening stones to real expensive flattening stones.
Yup, that'll work,
abrasive grain/grit on a piece of glass or a tile or another stone is about as basic and advanced as it gets,
theoretically available for $1-$3,
the $0-$1 version is loosen grain from your existing stone,
so the steps are,
mark stone surface up with a pencil , its flat when pencil marks are gone,
use a nail to scratch the surface and loosen some grit,
followed by a short 10-20 second rub (figure eight movements) with lube (water or oil whatever you regularly use) on another stone (dollar tree) or a brick or concrete or glass ...
thats all you need to condition/resurface stones like regular hardware store stone (sic or alumox, hard bond "oil stone")
if pencil marks are gone you're finished, you've just conditioned your stone, flush/wash and use for sharpening
if there is pencil left after 10-20 seconds, it needs flattening, so just keep rubbing until pencil is removed,
after its flat, then wash/flush the stone, and condition it (scratch with nail to loosen some grit, rub 10-20 seconds max , stop)
more detail in
How To straighten/flatten out a lansky stone ??
