Hi @SAS_L
Is the on-premise SAS platform on Viya as well? If not, there will be a lot of things that you will have to be considered during migration (data and content) based on the products you are licensed as the architecture and the way SAS 9 & Viya platform works is quite different. This SGF paper is good read for Planning for Migration from SAS® 9.4 to SAS® Viya®. Also, for SAS Viya I don't think we have any migration guide like 9.4 so it will be self research. you can also engage services from SAS to advise on the requirements you have.
If you are upgrading Viya on premise from lower version (3.3, 3.4) to latest 3.5, you will have to see on what tools customer has in order to replicate the on-premise environment to cloud and then there are few steps listed in the deployment guide to upgrade. If not, the only way would be to install a new environment on cloud and plan to move content and data to this new environment.