Excersise apps

Hey everyone! I’m 16 and I’m a dancer. I’m medium tall (5’3 1/2 ) and I way about 100 pounds. So you can imagine I’m skinny. I probably should have a little more muscle on me but my doctor says I’m not unhealthily skinny or underweight to where it’s a danger or anything. I have some muscle in my legs, especially in my calves. Not as much as I’d like to have but it’s not bad you know? Now my arms have like 0 muscle lol. So that’s where I’m really trying to get more muscle in because it will make my dancing look more clean and together. I already am neat with my dancing and I look clean but no matter what I do it naturally still looks a little flimsy bc i have no muscle on my arms. I take pointe so I definitely have gotten better at my core, but some core exercises would help too. Anyone know any good exercise apps I can use to just maybe help me gain some muscle on my arms b4 my recital? It’s June 1st so I have a little more than 2 months to get a little lol. Dancers if you know any don’t be afraid to comment too! Thanks!