So you are using Donor Perfect for these forms.
https://www.donorperfect.com/
So the next question will be how do you get those forms from them and onto your website?
Do you generate the forms through Donor Perfect and then get given a block of html code to add to your website?
Like on this page?
https://www.donorperfect.com/fundraising-software/integrated-online-forms/
If that is yes to above, then you can simply add that code to a html iframe or your page.
https://support.wix.com/en/article/using-iframes-to-display-visible-content-on-your-site
If you get given two blocks of html code that mentions you need to place the first part in your head section, then you need to look at putting it as a custom tool in your Tracking and Analytics section.
https://support.wix.com/en/article/embedding-custom-code-to-your-site
Otherwise, you could go down the harder yet more secure route and see if they have their own API that you can use with Wix with the use of Wix Fetch or Wix HTTP Functions.
https://www.wix.com/corvid/reference/wix-fetch.html
https://support.wix.com/en/article/corvid-accessing-third-party-services-with-the-fetch-api
https://www.wix.com/corvid/reference/wix-http-functions.html
https://support.wix.com/en/article/corvid-exposing-a-site-api-with-http-functions
Wix Example for exposing your site.
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-myapi-and-myapiclient
Or you can look into making up the user input forms yourself in Wix and have complete control over it all.