if you got a banner with missing winds slits, it is possible to add it on the spot with practically no tools or experience required. Just remember to be safe, cautious, and only use tools you’re familiar with and authorized to use.
First, we’ll mark the banner where the future cuts will fall. Never cut anywhere within 12 inches of any edge to avoid tearing. The best process is to measure about 12 inches off of the top edge and about 16 inches off of any side, and put a small mark there. Then, continue moving along the side placing marks every 16 inches. If your banner is two-to-three feet, you can add a second row of marks 12 inches off the other edge in a checkered pattern to the first row. On three-to-five feet tall banners, you perform a similar process with three rows of cuts, keeping the rows about 12-16 inches apart and never closer than 12 inches to any side or edge of the banner. Remember to keep your marks alternating between the rows in a checkered pattern.
After you're done with marking the banner, grab any solid round object with a 6-8 inch radius with enough height to safeguard your fingers. Usually a cereal bowl or large mug/cup works fine. Throw the bowl in the middle of your first mark, and while being careful and watching your fingers, make a half moon cut on the bottom end of the bowl. Do not cut all the way round and only go half way, keeping the top half of the circle uncut. Repeat the process for all the marks you made, and you’ve got yourself a perfectly cut wind slit banner ready for use.