How do I switch lead status in SFDC from "new" to "in progress" on follow up email in drip campaign?

Are you referring to the status for the Leads or the status of the SFDC campaign?

If you are referring to the Lead Status field value in the SFDC Lead record, you can create a smart campaign that is triggered by sending the drip campaign email and that has a Change Data Value flow action that will update the Lead Status field value.

If you are referring to the campaign member status in SFDC, you will have to define the desired status values in the corresponding Marketo channnel first and then synch the Marketo program with the appropriate SFDC campaign.  Then you would create a smart campaign that is triggered by sending the drip campaign email and that has a Change Program Status flow action that will update the program status to the desired value.  Marketo will automatically synch the update to the SFDC campaign member record.

In case your drip campaign is not within a Marketo Program, you can also run a flow action to change the SFDC Campaign status to "in progress"