The inter-dimensional extrapolator is a device that Cisco Ramon created; that allows Kara Danvers to travel from Earth Thirty-Eight to Earth One any time she wishes, as well as communicating with him.
Wishing to give Kara Danvers the ability to travel between Earths herself, Cisco Ramon created an inter-dimensional extrapolator. He gave it to her as a gift, also explaining that it had communication functionality. She later used it, opening a small breach from Earth One to Earth Thirty-Eight, traveling between them.
Sometime after, Winn Schott examined the device, being impressed by it. When the D.E.O. brought in a new prisoner, he hypnotized Kara, broke out of his handcuffs and took the inter-dimensional extrapolator, using it to transport himself to Earth One.