You can overexpose the background to pull out some shadow detail in your subject, or pick a background which itself is in shade.
You can add light with a flashgun (or several) or a reflector.
Possibly you can reposition the subject if you have that option.
Here's an example with some on camera direct fill flash. No edits other than a WB tweak and small crop...
Here's one using a flash and white brolly. No edits....
Here's one with natural light only, using a dark background in its own shade to allow the exposure to be set for a balance between the shaded areas and the sunlit grass. The grass is a little bright, which could be fixed, but overall I'm happy enough. No edits other than cropping....
Final example, overexposing the background and finding an angle where I at least get some light where I need it. No edits except cropping....
Personally I don't think I've ever used a reflector only, but there are plenty of examples on Youtube etc..