If you want to learn how to download Avast antivirus on an iPhone, simply follow the steps given below:
 On your iPhone, go to the app store and in the search box, type in ‘Avast Security and photo vault’.
 Now, tap the ‘download’ button and wait for it to finish.
 After the download has been completed, click on ‘open’.
 After reading the privacy policy and end user license agreement, tap on ‘not now ‘and click on ‘allow’.
These are the steps to download and install Avast antivirus for free on your iPhone.