Use the data from the next heaviest bullet you have. Maybe I'm ahead of myself, maybe you have load data for some other 55 grain bullet. If you have, just use that data, starting at the usual suggested starting load.
If you don't have loading data for any 55 grain bullet, then use the next highest bullet weight data you have. Since the data would be for a heavier bullet, the load would be light, so just start with it and work up.