Depending on the depth of the lines, I use either Juvederm or Bolotero. For thinning lines, this filler works great and has a natural result.
Any hyaluronic fillers such as Juvederm, Restylane and Bolatero will work
for your forehead lines. If you've never done it before you can start with
Juvederm and then try another one in 6-9 months and see which ones you like