Hi,
Thank you for choosing Master Slider.
I recommend you change your theme because to do that on twenty seventeen, it is not easy and it requires coding skills.
There is one easy way to do that, but it is not recommended because you will lose these settings after each theme update.
To do so, follow the below steps:
1. Choose the slider you want to have as a header.
2. At the bottom of the page, copy PHP function like the screenshot: https://support.averta.net/en/wp-content/uploads/MasterSlider27.png
3. Go to the folder of your WordPress website, then: wp-content\themes\twentyseventeen\template-parts\header, and open header-image.php
4. In the line 15 replace <?php the_custom_header_markup(); ?>
with the php function of your desired slider.
5. Save the file and see the result on your website.
6. If everything works fine and the slider appears at header, now you can change the slider sizing method (it is better to be full-width) and the slider height.
If you have any further questions, please let me know.
Best,
Averta