Hi there's a few ways to do this ,your using BGP so you could set the primary link to have a better local preference than the backup link , you can also use a route-map to specify which subnets to allow all traffic or just some subnets or alter 1 of BGPs other attributes as well , you could send them a less preferred(higher) MED for the backup link
or
you could use ip sla with tracking of specific routes across the primary and the use a route-map to set the ip next-hop if the route becomes unavailable and add the verify-availability on it to make sure the link you move too can definitely send traffic across the backup and reach the new verified route
EEM can be difficult to setup i would avoid it for something like this when there are easier options available
If this helps please mark as correct
Mark