Bundle Customization can be done in the Additional configurations settings of the app.
The product gets cropped during setup for some stores.
To fix this issue, navigate to Settings > Additional configuration for full page builder
Copy and paste the code below in the Custom CSS for bundle builder
.gbbProductImageContainerImg {
object-fit: contain !important;
}
OR
.gbbProductImageContainerImg {
object-fit: contain !important;
max-height: 100%;
max-width: 100%;
aspect-ratio: 1 / 1;
}