The cluster group SRVSQLCL1 already exists. To contine, specify a new sql server failover cluster group name

At the time of Cluster installation the given resource already used by Cluster. you will get below error

To resolve the issue.
1. Remove the given SQL Cluster name from Cluster Resource

Open the Failover Cluster Manager

Goto Roles or Services and Applications 

Right Click on the Resource Name and select Remove 

And then you can proceed with remaining Steps.

If you remove the cluster resource the associated cluster storage disk also goes offline as shown in below images.

Right click on cluster resource name and select remove option

it will remove the cluster resource and associated  disk from cluster and disks goes to offline also

then you need to add cluster disk by clicking Add Disk in right side pane

in add disk to cluster window select only cluster disk and click ok

this will add disk to cluster storage disks