Simply cut the new grommet with a razor blade, knife, etc, and roll it into the
hole.
Success will depend somewhat on hole size & size of the wire bundle in said hole.
Another approach is to use a short piece of hose, couple of inches long, slit it
down one side (lengthwise) fit it around the wires, slide into hole. Put a nylon
Ty-Rap around each end to prevent it sliding any farther. One side ty-rap
if it is a blind hole, just secure that tie to the bulkhead.
Remember.....a grommet is nothing more than a very short piece of hose designed
to prevent chafing.
Regards,
Zed/701/R912/90+%/etc