Configure tcp monitor port

I don't know about the powershell, but if its created and you require to modify it, use the CLI or the GUI, the below is the CLI way,

(cfg-sync Standalone)(Active)(/Common)(tmos) create ltm monitor tcp test1
(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm monitor tcp test1
ltm monitor tcp test1 {
    defaults-from tcp
    destination *:*
    interval 5
    ip-dscp 0
    recv none
    recv-disable none
    send none
    time-until-up 0
    timeout 16
}
(cfg-sync Standalone)(Active)(/Common)(tmos) modify ltm monitor tcp test1 destination *:8080
(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm monitor tcp test1
ltm monitor tcp test1 {
    defaults-from tcp
    destination *:webcache
    interval 5
    ip-dscp 0
    recv none
    recv-disable none
    send none
    time-until-up 0
    timeout 16
}
(cfg-sync Standalone)(Active)(/Common)(tmos)