element-plus/docs/examples/upload/manual.vue

<template>
  <el-upload
    ref="upload"
    class="upload-demo"
    action="https://jsonplaceholder.typicode.com/posts/"
    :auto-upload="false"
  >
    <template #trigger>
      <el-button size="small" type="primary">select file</el-button>
    </template>
    <el-button
      style="margin-left: 10px"
      size="small"
      type="success"
      @click="submitUpload"
      >upload to server</el-button
    >
    <template #tip>
      <div class="el-upload__tip">
        jpg/png files with a size less than 500kb
      </div>
    </template>
  </el-upload>
</template>
<script lang="ts">
export default {
  methods: {
    submitUpload() {
      this.$refs.upload.submit()
    },
  },
}
</script>