First create a new page in SitePages. Name it like "thanksForYourAnswer" and give some text and maybe a hyperlink to the homepage.aspx called "click here to get to start page".
After this create a text file (maybe script.txt) and enter this code:
window.location = "https://sharepoint.tld.de/departments/Site/_layouts/15/start.aspx#/SitePages/thanksForYourAnswer.aspx";
Save the text file and drop it to your SiteAssets library.
Copy the url to this uploaded text file.
Now click your survey list in site contents. Here you are in that location where the survey leads people who finished the survey. Edit the page (gear in right hand corner - edit) and add a content editor webpart. In content editor web part properties paste the link to your text file to make the web part run the script. End editing.
Now everyone entering that survey will be redirected to the url in the text file. You can enter survey settings by using the three dots on the survey app in site contents. If you want to end this behavior - just edit the script text file in site assets and comment the line for redirecting.
You can share the link for doing the survey by Newsfeed or on any other way as the users will be redirected if they try to enter the survey by clicking the app.