[SkunkBoat]

It will have to be in the garmin ".adm" file format in order to load into the unit from an SD card.
Get garmin Homeport software free from Garmin.
You "might" be able to import waypoints from your Lowrance SD card and then save as a Garmin adm file.

Lowrance might be a .gpx file type

I went from Lowrance to Garmin too but I seem to remember having a problem related to not having an SD card smaller than 2 GB. Unfortunately I have chronic "CRS" disease and can't remember how I got around it.

I actually just went thru my annual data cleanup in HomePort. I dump out my waypoints to an sd card as "2019data" then rename and edit new waypoints that are still default numbers

Even if you can't get them imported, it will be WAY EASIER to enter and edit them in Homeport using a PC and a keyboard rather than in the menu of the unit with buttons.
I had paper charts of artificial reefs and I entered every wreck/rockpile/subway car/tank I could find numbers for. When I get on a wreck, I mark the edges and high spot. If I get on something and my original entry was off, I mark the correct spot spot with a default waypoint and clean it up in Homeport over the winter. I have hundreds of waypoints.

You have Actice Captain available to you. I don't know if that is another way to get data in and out in different formats.