If you want to import longer videos, you can upgrade to PRO which supports up to 5 minute videos, recorded directly with your device's camera app, and saved to gallery (in-app purchase monthly or yearly subscription required).
Press the PRO icon at the top, and choose "PRO Editing - Monthly Subscription" or "PRO Editing - Yearly Subscription" and follow the in-app purchase steps. With the subscription you get to remove all advertisements from the app, import up to 5 minute videos from gallery, use the 3 x 3 frame, and personalize the watermark with your own name/text (up to 20 characters).
Once you've upgraded to the pro-trimmer, in the Trim Video screen, press the 5 minute button and then drag the slider (bluish circle above the filmstrip) all the way to the right - you should see the end time increasing as you drag it. This will allow you to import a longer video up to the end time you choose, or your video's duration (up to 5 minutes max).