How can I redirect my client to second form after filling out the first form?

If you need to chain the users into another form after filling the current form out, you can do it in two ways:

1. In case you need an unconditional/absolute redirect your submitters after filling out the form, please use "Confirmation Options" feature under "Form Settings" tab that can be configured to show either your custom text after a successful submission or redirect users to a custom "thank you" landing page/another form.

Locate the feature, click the "Redirect URL" choice and paste the URL of the landing page/your another form to redirect your customers to.

Form Options -> Confirmation Options -> Redirect URL

2. Another option here can be conditional redirect your users when a certain field equals to a certain value/option using "Logic" feature of your form.