Priority Group activation behavior

We have two pool members in a pool: server_1: with Priority:20 and server_2: with priority:10 the normal behavior, is when the server_1 goes down, then server_2 handles the traffic, and when server_1 goes up again, it handles all new connections, but the existent connections is still handled by server_2. we need to change that behavior, as when server_1 comes up, we need it to take all connections.

I've tried to use custom script to be run if a syslog triggered, as if server_1 goes up, delete the connections for server_2, as below, but it didn't work, i don't know what i miss

alert BIGIP_MCPD_MCPDERR_POOL_MEMBER_MON_UP "Node /Common/server_1 address 1.1.1.1 monitor status up." {
exec command="/usr/bin/tmsh delete sys connection ss-server-addr 1.1.1.2"
}