The Attribution models currently available in App + Web are the same as Firebase which are different to what you find in Universal Analytics. From what I can see there is also no option to create a custom model to suit your organisation’s needs.
You can currently select your attribution type in the main reporting UI by clicking on customize report icon and then choosing the Attribution Model of your choice from the drop down.
The Four Models as per Google’s Documentation
All attribution models in Analytics exclude direct visits from receiving attribution credit unless a conversion cannot be attributed to a campaign.
Cross-channel last click
App + Web looks at clicks from all sources and attributes the conversion to the last click. (Excludes direct*)
Cross-channel last engagement
App + Web attributes the conversion to the last click, or to an ad impression if there is no recent click. (Excludes direct*)
Google Ads preferred last click
App + Web attributes the conversion to Google Ads whether or not there is a click from another source. (Excludes direct*)
Google Ads preferred last engagement
App + Web attributes the conversion to Google Ads whether or not there is a click or ad impression from another source. (Excludes direct*)