Unserializing a repeating text field

There is not a user interface to change the storage format.

There is a save hook, which can be used to write another field value based on the value of the repeating field: https://docs.pods.io/code/action-reference/pods_api_post_save_item/

The following plugin will cause a repeating text field named multiple_text_entries to be saved as pipe-separated values in field multiple_text_entries_pipe_separated when the post is saved:

<?php
/**
 * Plugin Name: Save field as pipe-separated values
 * Description: Saves a repeating text field as a pipe-separated string when saving.
 */
add_action(
    'pods_api_post_save_pod_item',
    function ($pieces, $is_new_item, $id ) {
        $repeating_field_name = 'multiple_text_entries';

        if ( array_key_exists( $repeating_field_name, $pieces['fields'] ) ) {
            $entries = $pieces['fields'][ $repeating_field_name ]['value'];
            if ( ! is_array( $entries ) ) {
                $entries = [ $entries ];
            }

            $entries = array_map( 'trim', $entries );
            update_post_meta(
                $id,
                $repeating_field_name . '_pipe_separated',
                implode( '|', $entries )
            );
        }
    },
    10,
    3
);