Explanation
Below are the steps you need to perform in this scenario. Refer the link mentioned in the reference section.
Download the installation file for the Azure Site Recovery Provider
To set up the source environment, you create a Hyper-V site and add to that site the Hyper-V hosts containing VMs that you want to replicate. Then, you download and install the Azure Site Recovery Provider and the Azure Recovery Services agent on each host, and register the Hyper-V site in the vault.

Download the vault registration key
Download the Vault registration key. You need this when you install the Provider. The key is valid for five days after you generate it.

Install the Azure Site Recovery Provider on Host1.
Install the downloaded setup file (AzureSiteRecoveryProvider.exe) on each Hyper-V host that you want to add to the Hyper-V site. Setup installs the Azure Site Recovery Provider and Recovery Services agent on each Hyper-V host.
Register the server
In Registration, after the server is registered in the vault, select Finish.
References:
https://docs.microsoft.com/en-us/azure/site-recovery/hyper-v-azure-tutorial