Hi @shri19 ,
This will work in same way like configuration of normal image configuration work.Please refer to Media section of below link and there you will find the option of adding link for bundle image.
https://experienceleague.adobe.com/docs/campaign-standard/using/communication-channels/in-app-messaging/customizing-an-in-app-message.html?lang=en
Also the In-App Message full-screen template supports showing an image from a remote server (Image URL) or from the app bundle (Bundled Image). The image should be in a standard image format, for example, JPG, GIF, or PNG.
Due to device screens having many different dimensions, the image probably not fit exactly into the space provided by the template. The template always focuses on showing the center of the image and crops (portrait) or fades (landscape) the sides if the image does not fit.
Here is the exact placement and sizing rules for each orientation:
Portrait, where the image is scaled to height of 195px for phone, 529px for tablet, centered if image width is smaller than device width, and cropped if image width is greater than device width.
Landscape, where the image is scaled to 100% of height of device, width is 75% of the device, and with a fade out on the right.
If you have issues with the full-screen template, you can download and use the Custom HTML template. The Custom HTML template provides greater flexibility for images and allows full control of the template.
Ref Link :- https://experienceleague.adobe.com/docs/mobile-services/using/messaging-ug/inapp-messages/in-apps-ts.html?lang=en