You can use the background removal feature to separate the object from the background and easily make the background transparent.
Open ① Tool Select window and select ② Filter.
Tap ① AI and select ② Background Removal.
Immediately after activating the background removal feature, it will be in the mode to specify the object. Tap the screen and specify the object you want to cut out. A ① blue knob will be displayed at the tapped point, and the target will be selected in blue.
If there is an unnecessary part selected, select the ① - (minus) button to switch to the background selection mode. When you tap the area you want to treat as the background, a ② red knob will be displayed and you can exclude it from the selection range.
When you turn off ① Show Mask, you can check the state after cutting out the object. When you are done with the adjustments, tap the ② OK button.
The background has been removed.