Hello and welcome to our Community, @phantrung92.hn ,

look here but only in german:

https://www.telekom.de/hilfe/vertrag-meine-daten/meine-daten/umzug-adressaenderung

@phantrung92.hn 

You have two options, based on German telelommunication law:

1. you cancel the contract and after cancellation you must pay up to further 4 months; then you are completely flexible which tariff or provider you choose for the new flat
   Precondition for this path is that you officially order that the existing contract shall be continued at the new address without any alteration of contract content or duration; Telekom accepts such orders only on the phone or in a Telekom shop
   
2. you continue the contract at the new address however with slightly different scope and with a new contract period of 24 months, and hence you do not need to pay for the old address once the DSL is up and running at the new address
   This is possibly easier to order since for this path Telekom also accepts online orders
   https://www.telekom.de/hilfe/umzug/allgemein/internetanschluss-umzug