I was able to successfully upload images in my MongoDB project using Multer, but I'm stuck on how to update them. When I tried using the same trick in my Edit function, the log says I can't set headers after they're sent to the client. For context, I'll put in my code for uploading and editing

router.get('/upload', IsLoggedIn, (req, res, next) => {
    res.render('mods/upload', {title: 'Upload a mod', user: req.user});
    res.sendFile(path.join(__dirname, './mods/upload.hbs'));
});

router.post('/upload', upload.single('image'), IsLoggedIn, (req, res, next) => {
    console.log(req.file);
    Mod.create({
        name: req.body.name,
        image: req.file.filename,
        file: req.body.file
    }, (err, newMod) => {
        if (err) {
            console.log(err);
        }
        else {
            res.redirect('/mods');
        }
    });
});

router.get('/edit/:_id', IsLoggedIn, (req, res, next) => {
        Mod.findById(req.params._id, (err, mod) => {
            if (err) {
                console.log(err);
            }
            else {
                res.render('mods/edit', {
                    title: 'Edit mod',
                    mod: mod,
                    user: req.user
                })
            }
        }).sort({name: 1});
        res.render('mods/edit');
        res.sendFile(path.join(__dirname, './mods/edit.hbs'));
    });

    router.post('/edit/:_id', upload.single('image'), IsLoggedIn, (req, res, next) => {
       Mod.findOneAndUpdate(
            {
                _id: req.params._id
            },
            {
                name: req.body.name,
                image: req.file.filename,
                file: req.body.file
            },
            (err, updatedProject) => {
                if (err) {
                    console.log(err);
                }
                else {
                    res.redirect('/mods');
                }
            }
        )
    });

Am I even able to update images in the same fashion, or is there something entirely different I should be doing? I'm still super new to Multer and I haven't done a whole lot with MongoDB, so any guidance would be super appreciated!