Workflow to remove String # from lookup Column and copy lookup column value to text column on the same list

In SP Designer go to your list workflow and create a workflow

create a variable name it I name my variable DeviceName

Set variable DeviceName to the value of your lookup column

Than use Replace Text in find give the following regular expression: \d*;#

in Replace With give just space and click ok

and in Store in create another variable and store the cleaned values

the use Set field in current Item

and set the text field column with the new cleaned variable value see screen shot of workflow