This shows how to set custom values to repeatable fields created by Admin Page Framework.

demo-custom-repeatable-field-values.php

<?php
/* Plugin Name: Admin Page Framework - Setting Custom Repeatable Field Values */ 

if ( ! class_exists( 'AdminPageFramework' ) ) {
    include_once( dirname( __FILE__ ) . '/class/admin-page-framework.min.php' );
}
    
class AFFTest_CustomRepeatableFieldValues extends AdminPageFramework {

	public function setUp() {

		$this->setRootMenuPage( 'Settings' );	// where to belong
		$this->addSubMenuItem(
			array(
				'title' => __( 'Custom Repeatable Field Values', 'demo-custom-field-values' ),	// page and menu title
				'page_slug' => 'apf_demo_custom_repeatable_field_values'	// page slug
			)
		);
			
		$this->addSettingSections(	
			array(
				'section_id'	=>	'custom_repeatable_values',	
				'page_slug'		=>	'apf_demo_custom_repeatable_field_values',	
			)
		);
		
		$this->addSettingFields(
			'custom_repeatable_values',	// the target section ID
			array(	
				'field_id'		=>	'my_text_field',
				'title'			=>	__( 'Text Input', 'demo-custom-field-values' ),
				'type'			=>	'text',
				'repeatable'	=>	true,
				'value'	=>	'one',
				array(
					'value'	=>	'two',
				),
				array(
					'value'	=>	'three',
				)				
			)
		);
		
	}
			
		
	/**
	 * Do something in the page.
	 * 
	 * @remark	This is a pre-defined framework method.
	 */
	public function do_apf_demo_custom_repeatable_field_values() {	// do_{page slug}
			
		submit_button();	// Add a submit button
	}
		
	/**
	 * The pre-defined validation callback method.
	 * 
	 * @remark	This is a pre-defined framework method.
	 */
	public function validation_apf_demo_custom_repeatable_field_values( $aInput, $aOldInput, $oAdminPage ) {	// validation_{page slug}
		
		// See the log file in the wp-content directory.
		// AdminPageFramework_Debug::logArray( $aInput );
				
		$this->setSettingNotice( 'This is a test message.', 'updated' );
		
		return $aInput;
		
	}
    
}
new AFFTest_CustomRepeatableFieldValues( );