To create subnet, make sure there is no existing tailscale installation in the network that also allow similar subnet access.  

If there is, there is need to disable the subnet access first before creating new one as follows

1. Login as admin

2. Click 3-dots next to machine name with subnet

3. Click Edit Subnet Route

4. Uncheck the subnet

5. Save

6. Go to the machine where there is subnet route enabled

7. In command prompt, type:  
<code>
tailscale up --reset
or best 
tailscale up --accept-routes --advertise-routes= --reset
</code>
8. In new machine, go to command prompt, type:
<code>
tailscale up --accept-routes --advertise-routes=192.168.x.0/24 --reset
</code>
9. From TailScale admin console, select the machine name and enable the subnet from the Edit Subnet Route menu