If you don't have an Android or a compatible iPhone, then the best solution is generally to try borrow one from a friend or family member.
Getting these signal measurements is crucial in helping you find the right booster for your situation, and there's no real alternative to performing these tests, so it's usually worth calling in a favor to help with this step.
If that isn't possible, then the next best thing is to just run a speed test on any cellular device, and send us screenshots of those readings. It's definitely not as good as a proper field test, but it's a start.