An iRule to redirect one URL to an another URL

You don't need to use an iRule for this - you can use a traffic policy: https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/local-traffic-policies-getting-started-12-1-0/1.html

To do this with an iRule you can try

when HTTP_REQUEST {
    if {[string tolower [HTTP::uri]] equals "/l3/ws1/aust_quality"} {
        HTTP::redirect https://abc.sharepoint.com/sites/L1_AUST_Quality.
    } 
}