Take a look at how to add a text field to a WooCommerce product so that your customers can add text.
This is a simple example of how to insert an add-on field to WooCommerce. You’ll need to install and activate WooCommerce Product Add-Ons first. Then go to the product where you’d like to add your field.
In the Product Data section, click Add Group, then Add Field.
Choose ‘Text’ for your field type then add a label to display alongside the field. You can add a price to the field if you wish; you can also specify whether the field is required – meaning the user must enter a value.
For text fields, there are some other parameters: for example, you can set a minimum and maximum number of characters and specify whether you wish to charge per character.
In the Pro version of the plugin, you can even specify whether to allow a certain number of free characters or whether you’d like to charge for alphanumeric characters only.
You can get the plugin here: https://pluginrepublic.com/wordpress-plugins/woocommerce-product-add-ons-ultimate/