@Moritz04 It sounds like you have successfully enabled one-time codes as a login method on your Strava account. If this is the case and you are able to successfully login using a one-time code, you will be able to navigate to the Settings page in the Strava app or on the Strava website to update your email address.
When updating the email address on your Strava account, you will first be asked to provide a one-time code sent to the email address currently associated with your account. Once that code has been successfully provided, you will be asked to provide the new email address which will also be sent a one-time code. Successfully providing the one-time code sent to the new email address will associate the new email address with your Strava account.
If you are running into error messages when attempting to update your email address, it may be the case that you have attempted the process unsuccessfully too many times in too short a period of time, causing a limit to be hit. We recommend waiting until the following day to attempt the change one more time.
If further trouble continues, it may be necessary to reach out to our Support Team for further help.