What is the correct notation to eliminate the time error?
Well, keep in mind that proofreading identifies things that could be errors, not necessarily things that are errors.
In this case, the music as written has only 3 beats in bar 4, which has a 4/4 meter, so the warning is appropriate. You could fix it by inserting a hidden 3/4 time signature in that bar – but then Dorico warns you that you have a hidden time signature, as well as a repeated time signature.
You could also choose not to go into 3/4 until the following measure – depending on the context, it may not be significant that the pickup itself is in 3/4, since it would be a pickup even in 4/4. (Of course, this may not be a possible choice if you’re not the composer.)
Or you could just ignore the warning! 
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I would write 3/4 a bar later. If you want a barline inside the last 4/4 bar, you can place an extra barline everywhere you want. I would probably make it a dashed or double barline, so that the musicians don’t get confused. 