Good call out Brian for those new to EXOS.
Vignesh, the idea behind the Default VLAN was that you didn't need to configure a VLAN in EXOS to use the switch. All ports are in the VLAN Default, thus if you were looking for quick Layer-2 solution...away you go. Didn't need to configure a VLAN.
So, as Brian rightly calls out, if your first step is to build a VLAN you first have to remove the port from VLAN default. A quick example from GTAC Knowledge:
https://gtacknowledge.extremenetworks.com/articles/Q_A/Which-command-is-used-to-add-ports-to-a-vlan
As Drew says....welcome to the Hub Community. Glad you joined us.