The lens distortion filter for Affinity Photo can be found in the distort sub-menu (which can be found in the filter menu). You can find the live version in the layer menu and live layer section
Go to the effect and set distortion and click the apply The effect is great for correcting lines by applying subtle settings. You can also apply larger values to really warp the image in both directions, you can you can set the value positive or negative and the default is 0. You can also interactively change the origin point.
It can be used multiple times and combined in 1000s of ways with the other filters that come with the powerful graphics application, Affinity Photo. Apply it multiple times with the same setting via the repeat at the top of the menu.
You can use it with channels so you can apply different values for the red channel as well as the green etc
This tool can be used to warp but it is also designed for corrections of lens, to add subtle tweaks to the image to correct errors
You can also use the effect on layers. Select something in the image and copy and paste then apply the effect to that artwork instead of the background.
You can record the settings and play it back via the macro panel
You can fade the results of the effect via the fade command found in the layer menu and add in a blending mode as well such as applying the effect as a darken or difference or pin light etc
You can also use it with selections, so add the effect to one selection and add a different effect to another selection to create an interesting design
You can also use the effect via the non destructive effects in the live layers in the layer menu. Select the layer and then apply the live effect and set the origin point as well as setting (-100% to 100%) as well as adding in blending mode such as darken and lighten and difference etc and set the opacity. You can also merge it with the current layer. You can also select no layers and apply the live layer and all the layers below will be modified by the warp. You can then move the live layer to a lower layer so all layers above will not be affected.
You can apply the effect to warp the image and then turn that design into a pattern layer via the layer menu and new pattern layer from selection. You can then apply the same effect to the layer. You can also rasterize the layer via the layer menu and then apply the effect to that layer.
You can use the effect with shapes, to warp them in all kinds of ways. The end result does depend, of course, on the shape
Text can be modified as well using the effect