Hi RPA,
1) For that you need use IDENTITY_INSERT, Once you set it on you can insert identity value as well.
SET IDENTITY_INSERT dbo.TableName ON;
2) You can get Max value of Identity or IDENT_CURRENT('tableName') and Just add 1 to It and then Insert Data.
IDENT_CURRENT('tableName')
or
MAX(Id)
3) Once you done with Insertion of Data you can set IDENTITY_INSERT it off.
SET IDENTITY_INSERT dbo.TableName OFF;
Refer below article
https://msdn.microsoft.com/en-us/library/ms188059.aspx
I hope this will help you out.