There is no button and there is no support for this game, period

[AWOL]

There is more information about which accounts are able to be converted here:

How do I change between the Steam and Funcom Client?

Steam Client vs Funcom Client The only difference between the Steam client and the Funcom client is how the client itself is accessed. The steam client must be used with Steam accounts through the Steam client. The Funcom client can be used with any Funcom account and accessed through account.secretworldlegends.com. Accounts that were originally TSW accounts will be able to covert from Funcom to Steam or from Steam to Funcom ONCE. Accounts made after the launch of SWL are NOT eligible to be …