Welcome to Nestwell Property Managements 24/7 DIY Maintenance Center. Thank you for your question about your running toilet.
Generally, when a toilet runs it's caused by too short of a chain on the flapper, or by a flapper that needs to be replaced. There is a separate article detailing how to replace a flapper here: http://help.nestwellpropertymanagement.com/en/articles/5011596-toilet-is-running.
The following video will show you how to adjust the flapper chain:
If you need additional assistance, please log in to your Resident Portal and Request a Repair.
Please be aware, if a vendor is required to attend to the issue, and an adjustment of the chain is the resolution, trip fees, and other associated fees will be applied to your tenant ledger in the month following the vendor's visit.