There's actually a funny story to what filter I used for this photo. I'll put it below.
The filter you want should be something like an ND 10000 or something along that line. You can search Amazon for solar filters. Then you'll just need one that matches the size of your lens. It'll probably cost between $20 and $30.
When I took this picture, I messed up massively. Rental and I accidentally bought the wrong filter size for it. The 500 mm uses the 40.5 mm drop-in filters. I bought a 50 mm filter on accident. I freaked out pretty good when I realized I wasn't going to be able to take a picture of the eclipse, but I found a solution. Those cheap filters that you put in front of your cell phone. I ended up cutting up one of those filters and taping it to the filter holder for the lens. This is far from ideal since that filter won't be able to handle heat for very long. I covered the lens whenever I wasn't taking photos to make sure that I didn't burn a hole through the filter. After taking all my photos and removing the filter, I saw that I had indeed scorched it a bit, but it held long enough for me to get some decent photos. Moral of the story is double check what size filters you need XD