First, import the certificate via MMC to the local computer > Personal store. After importing the certificate, go to 'Programs and Features' > Choose 'Windows Admin Center' and click 'Change'. It will open the installation wizard where you need to click 'Change' and can enter the thumbprint of the new certificate.

https://windowsserver.uservoice.com/forums/295071-management-tools/suggestions/33950335-how-do-windows-admin-center-change-certificate