How you can change the Lifecycle Stage of a list of Contacts in HubSpot

In HubSpot, you can change the lifecycle stage of contacts with workflows and also with import.

Go to Workflows in your HubSpot account.
Click Create workflow.
Select Start from scratch, then click Create workflow.
Set enrollment triggers. If you want this to be a one-time process, select manually so that contacts are only enrolled when you decide to add them.
Click the plus (+) icon to add a workflow action.
Click Set contact property value in the right panel, then select Lifecycle stage as the Contact property and choose the lifecycle stage value that you want to assign as the New property value to your list.
Click Save.
Click Review in the upper right, then click Activate to turn the workflow on.

Go to Contacts > Lists in your HubSpot account.
Click the name of the list to add to the workflow.
Select the checkbox at the top left of the list table to select all the contacts in the list.
Click the dropdown More and select Enroll in workflow.
Click the dropdown Enroll x contacts in this workflow and select a workflow, then click Enroll.

Create a .csv file that also includes the email addresses of the contacts you want to change the lifecycle stage for. Include a column for the lifecycle stage contact property and enter the new value you want for your contacts.
Go to Contacts > Contacts in your HubSpot account.
Click Import.
Click Start an import, then select File from computer .
Select Contacts as your import type, then click Next.
Select a file to import, then click Next.
The Lifecycle Stage column should automatically match with the lifecycle stage property in HubSpot.
Click Next.
Enter a name for your import, select the checkbox to confirm each statement, then enter your initials.
Click Finish import.

Once the contacts are imported, they will have their lifecycle stage changed to the selected lifecycle stage.