Yeah just use the API, if you have the record id that's all you'll need and then you'll need a code snippet that set's the record to approved

So just like this and I'm done?

//Get record and form by recordID in the url params
ApproveRecord ar = new ApproveRecord();
ar.Execute(record, form);

That would be splendid :D

Hm apparently yes and no. I'm struggling to find a way to actually be able to use that snippet. I apparently can't use it in Razor, so what are my options to approve a record? Is there a way in razor? Or how can I do it without Razor?

You can run any code in razor, because it is effectively C#. Unfortunately, the code snippet you have there isn't correct. You may want to checkout the Umbraco Contour Documentation and read up on how it works. Tom Fulton has a good code sample on gist. Here's another one:

@using Umbraco.Forms.Data.Storage
@using Umbraco.Forms.Core.Services

var recordId = Request["recordId"];
if (!string.IsNullOrWhiteSpace(recordId))
{
    var guid = new Guid(recordId);
    using (var storage = new RecordStorage())
    {
        var record = storage.GetRecord(guid);
        using (var service = new RecordService(record))
        {
            service.Approve();
        }
    }
}

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