Hello @ana,
My name is Henry and I am happy to assist with your inquiry, and appreciate you contacting LastPass Support!
I am sorry about the issues you are having with your account. Our records show that you don't have any device switches left for your account which is why you could not complete the switch. I have added an additional device switch as a courtesy so you can switch to desktop. Please remember that once you switch, you will no longer be able to return to using mobile.
Thank you,
Henry | Customer Care