go an buy an electronic tuner! (don’t buy a “cheap” noname one - you can get a good one for 10 - 15 $ / € e. g. the Korg clip tuner) - then learn how to use it to tune your mandolin - it’s not that difficult. Just always lower the string until it is a bit too low, then tune upwards until it’s ok - never from high to low - that’s not stable).
You can later learn to tune by ear - it’s good if you learn this too.
Read something about the setup of your mandolin - check my website www.mandoisland.de ! It looks like your bridge might be a bit too much slanted