I'm somewhat new to Nintex. Using Nintex Workflow 2013 and Forms, I'm trying to add multiple values into a multi-choice lookup column. I can get the workflow to add the first item, but not any subsequent choices. What am I missing?

Here are the details:

I have a list at the root site collection, RootListA, and let's say it contains offices (OfficeA, OfficeB, OfficeC, etc.). Also in the root site, I then created a lookup site column called SiteColumnA; it's pointing to the Title field of RootListA.

Now, in a sub-site I have another list called SubSiteListB. I added the SiteColumnA lookup column as a column in SubSiteListB.

At the subsite level, I have a site workflow with a Nintex form. The form has a multi-choice lookup field pointing to the Title column of RootListA. The ID is connected to a workflow variable, txtOffices, a single line of text. Once the form is submitted, the workflow creates a new item in SubSiteListB. I want the workflow to add every Office that was selected into SiteColumnA in the SubSiteListB list.

When I log the txtOffices variable, it's in this format: 1;#OfficeA;#3;#OfficeC. I've tried using the Create Item and Update Item actions, setting the field SiteColumnA to txtOffices. This results in SiteColumnA being set to OfficeA, not OfficeA and OfficeC. So I'm assuming these would be the wrong actions to use. What should I try next?

Let me know if any clarification is needed or if this has been answered already.

Thanks in advance!