How to integrate two objects underwent SCTransfrom?

[alohaia]

Say I have 2 conditions, each of which has 3 samples. Now I have merged and integrated samples of each conditions as descripted here, and then finally ploted UMAP plots.

# Read10X
# ...

zao <- merge(x = zao10, y = c(zao1112, zao13), project = "TLSZAO",
             add.cell.ids = c("zao_10", "zao_1112", "zao_13"))
wan <- merge(x = wan5, y = c(wan7, wan13), project = "TLSWAN",
             add.cell.ids = c("wan_5", "wan_7", "wan_13"))

next_analysis <- function(obj) {
    obj[["percent.mt"]] <- obj |> PercentageFeatureSet(pattern = "^mt-")
    obj  <- obj |> subset(subset = nFeature_RNA > 500 & nFeature_RNA < 6000 & percent.mt < 5)

    obj <- obj |> SCTransform(vars.to.regress = "percent.mt")
    obj <- obj |> RunPCA()

    obj <- IntegrateLayers(obj, method = HarmonyIntegration, normalization.method = "SCT",
                           orig.reduction = "pca", new.reduction = "integrated.harmony")
    obj <- PrepSCTFindMarkers(obj)

    return(obj)
}

zao <- next_analysis(zao)
wan <- next_analysis(wan)

prep_visualization <- function(obj) {
    obj <- obj |> FindNeighbors() |> FindClusters() |> RunUMAP(dims = 1:10)
    return(obj)
}

zao <- prep_visualization(zao)
wan <- prep_visualization(wan)

DimPlot(zao, reduction = "umap")
DimPlot(wan, reduction = "umap")

Now I want to merge zao and wan to perform integration. How could I do this?