Converting comma-separated string to multiple tags in Sanity

{
      name: 'tags',
      title: 'Tags',
      type: 'array',
      of: [{type: 'reference', to: {type: 'tag'}}]
    }

const query = `{
  "tags: *[_type == "tag"]{_id, title},
  "posts": *[_type == "post"]
}`

//fetch all tag and post documents
const {tags, posts} = await client.fetch(query)

//loop through all posts
posts.forEach(post => {
  //split the string of tag titles you have and return an array of refs instead
  const tagRefs = tagString.split(',').map(title => {
    const tag = tags.find(tag => tag.title === title)
    return {_type: 'reference', _ref: tag._id}
  })

 //patch the post with the new array of tag refs
  client.patch(post._id).set({tags: tagRefs}).commit({autoGenerateArrayKeys: true,})
})

sanity exec ./path/to/script --with-user-token