Are you thinking of tiles for patterns etc?
Then hereīs a popular method:
Filter>Other>Offset, offset a fixed value for x and y that you can remember again (I donīt remember if it takes percentages these days, but try 50%).
Use the Rubber Stamp (clone) Tool to erase/blend in the seams.
You can now either offset the tile back to its original position (revert values from before with Offset filter), or leave it as it is. - Itīs now a seamless tile.