Let us welcome Mr Gary Li, a new member join BJ Office as Manager on June 8?帮忙看看有没错误吧.谢谢

Join改joining或who will join,要不就两个谓语了。还有,改8th。楼上的join是错的。

Let us welcome Mr Gary Li, a new member joins BJ Office as Manager on June 8th

1》a new member 是第三人称，而当时语境是现在时。
2》表示日期应该是 月份+数序数词
正确的应该是
Let us welcome Mr Gary Li, a new member joins BJ Office as Manager on June 8th.

Let us welcome Mr Gary Li, who will join BJ Office as Manager on June 8th.