suggestions on easy way to add location data to jpegs that will be recognized in iPhone

I have lots of .jpegs taken either w/ iPhone (location data turned off) or DSLR w/ no location data. Id like to find an easy way to add the locations to photos so that when synced to iPhone, photos will be searchable by location and show in map on iPhone. I do not use apple iPhoto app or whatever it might now be called. Now using last version Catalina

Suggestions? Tks much.

After saving image to Photos, open the photos app and double click on your image. This opens your image in a new window. You get a window like the one shown below.

On the top right of the image is a group of icons. Select the first one. See below.

When you select the first icon - a circle with the letter i in it you get a new pop up as shown below.

As you can see at the bottom of this pop up is an area to assign a location. While this may seem tedious, once you go thru it you'll see how simple it is.

There is an open source item called exiftool which will let you add location data and a lot more to files.