Redirect EDD license renew request to Freemius

sp-edd-fs.php

<?php

add_action('add_meta_boxes', function(){
	add_meta_box('sp_edd_fs_metabox', 'Freemius data', 'sp_edd_fs_metabox', 'download', 'side', 'default' );
});

function sp_edd_fs_metabox( $post ){

	$plugin_id	= get_post_meta( $post->ID, '_sp_edd_fs_plugin_id', true );
	$coupon	= get_post_meta( $post->ID, '_sp_edd_fs_coupon', true );

	echo '<p><label for="_sp_edd_fs_plugin_id">Plugin ID</label><input id="_sp_edd_fs_plugin_id" type="number" value="' . esc_attr( $plugin_id ) . '" name="_sp_edd_fs_plugin_id"></p>';

	echo '<p><label for="_sp_edd_fs_coupon">Coupon</label><input id="_sp_edd_fs_coupon" type="text" value="' . esc_attr( $coupon ) . '" name="_sp_edd_fs_coupon"></p>';
	echo '<p class="description">Set a coupon if you want to give users a discount</p>';
}

add_filter( 'edd_metabox_fields_save', function($fields){
	$fields[] = '_sp_edd_fs_plugin_id';
	$fields[] = '_sp_edd_fs_coupon';
	return $fields;
});

add_action( 'template_redirect', function(){
	if( ! function_exists( 'edd_is_checkout' ) || ! function_exists( 'edd_software_licensing' ) ||  ! edd_is_checkout() ){
		return;
	}
	$license_key = isset( $_GET['edd_license_key'] ) ? $_GET['edd_license_key'] : '';
	$download_id = edd_software_licensing()->get_download_id_by_license( $license_key );
	if( ! $download_id ){
		return;
	}
	$plugin_id	= get_post_meta( $download_id, '_sp_edd_fs_plugin_id', true );
	$coupon	= get_post_meta( $download_id, '_sp_edd_fs_coupon', true );
	if( !$plugin_id ){
		return;
	}
	$args = [
		'license_key' => substr( $license_key, 0, 32 ),
	];
	if( $coupon ){
		$args['coupon'] = $coupon;
	}
	$url = add_query_arg( $args, "https://checkout.freemius.com/mode/dialog/plugin/{$plugin_id}" );
	wp_redirect( $url );
	exit;
});

After added this code to child theme's functions.php (or in any custom plugin) you will see 2 new options in EDD download edit page under heading "Freemius data". Get those values from freemius and add there.
Also check license key formation if you need to change. As freemius support 32 characters license key, so i used substr( $license_key, 0, 32 ). You can change it according to your requirement.