If the FM signals are overwhelmingly strong relative to the digital channel 6 signal, the tuner can't sort it out. Nothing you can really do about it easily, depending on the operating frequency(ies) of the FM stations. If the FM frequencies are not too close to the low end of the band, one can filter them.
We discontinued and liquidated remaining inventory of our old 3-element FM antenna awhile back due to low (almost non-existent) sales. It was actually a very decent performer for channel 6. You can still pull up a data sheet for it cached on our website at
https://www.antennasdirect.com/cmss_...ibrary/FM3.pdf
A search of ebay shows that the 3FM can be found offered for sale by someone who ended up with some of those liquidated antennas. See
https://www.ebay.com/p/Antennas-Dire...enna/691182863 We don't have any connection with the seller.