This link shows you how:
Kaye: maybe this will help. ...enjoy the outdoor fun!
Here's a twist on a repair that might work for you.
It's really easy! Here are some sites to get you started.
And a visual:
I have a couple beach sand chairs that I re-web every few years.
A YouTube tutorial for a macrame solution!
This may help: https://happydealhappyday.com/fix-broken-canvas-porch-swing/
There are many different types of 'webbed' patio furniture.
Please post a picture of yours so that can see what style it is, and how the webbing is attached to the frame.
Photo is below. Thanks
Thank you for the photo, as it shows that your settee is not really webbed in structure, but is wicker, with webbing to support the seat cushion.
IMO the webbing is sagging because:
-it was not pulled tight enough when installed to the frame
-there are too many gaps in between the strips
-there is an insufficient number of strips
-the fabric composition of the webbing is one that either stretches, or too easily becomes weakened
Replacing the webbing is a fairly easy project:
5.Push the frame back into the setee.
My suggestion is to use nylon webbing, which is very strong and durable. Stores that sell outdoor hiking and climbing gear usually have a good selection of different thicknesses and widths.